At least two actuators families, one based on the rack-and-pinion principle and the other based on the lever arm (“Scotch yoke”) principle are known.
These two families are set: once the devices are manufactured and mounted in their casings, no adjustment of the transmitted torque is possible, with the risk of unsuitability to the operational requirements.
In the rack-and-pinion case, the torque is constant throughout the actuation. In the mechanism with a scotch yoke, the torque changes according to the variation in radius of the thrust axis relative to the axis of rotation. This variation is set and can only be changed by replacing the part with another one.
Among the methods of the aforementioned type, the document EP 0103744 discloses a solution where a valve can be opened and closed, using a rack meshing with a toothed elliptical rotating pinion, with the rack extending generally transversely to the axis of rotation of the pinion, following a curve which is the involute of at least a part of the primitive perimeter (or the diameter) of the pinion, with the pinion being connected with a sleeve so that one transmits a torque to the other.
A problem remains however as to the adaptation of the torque to the operational requirement to be met.